Adsorbent cartridge with accurate visual indicator

ABSTRACT

A cartridge comprising layers of adsorbent sheet is described. The cartridge includes an indicator that characterizes the consumption state of the adsorbent within the cartridge. The indicator is applied in a way such that discrete areas of indicator are visible. These discontinuous areas of indicator may be applied to the outside surface of the cartridge. Alternatively, the discontinuous areas may be formed by cutting windows in the outermost layer of the cartridge and either coating indicator on the layer beneath the window, placing an indicator layer between the window and the layer beneath it or filling the window with an indicating plug of material so that the indicator is visible from the outside of the cartridge. The indicator layer and indicator plug embodiments allow the use of any indicator with any adsorbent.

This application is a continuation of U.S. application Ser. No.16/343,705, filed Apr. 19, 2019, which is a 371 of InternationalApplication No. PCT/US2017/057592, filed Oct. 20, 2017, which claims thebenefit of priority of U.S. Provisional Application No. 62/411,409,filed Oct. 21, 2016, which are incorporated herein by reference in itsentirety.

TECHNICAL FIELD

This application relates to adsorbent cartridges having discrete areasof visual indicator for indicating the consumption state of theadsorbent within the cartridge in an accurate manner.

BACKGROUND

During surgical procedures anesthetic agent may not be entirely consumedand in such cases air exhausted by the patient can be recycled. Thisallows for the efficient use of anesthetic, as well as avoiding needlessrelease to the atmosphere, where many anesthetic agents can contributeto global warming. In order for a patient to rebreathe their exhaustedair, exhaled CO₂ must be adsorbed. This is achieved by passing therecycled air through a CO₂ adsorbent comprising calcium hydroxide orlithium hydroxide or mixtures thereof (sodium hydroxide is often used incombination with calcium hydroxide to catalyze the reaction to calciumcarbonate). In order to determine how much of the adsorbent has beenreacted, granular adsorbent materials are typically coated with aslittle as 0.001 w/w % indicator dye that changes color when theabsorbent is reacted (U.S. Pat. No. 7,476,641). In the case of calciumhydroxide, the color change occurs because of the decrease in pH due tothe conversion of calcium hydroxide to calcium carbonate, as well as theshort term consumption of sodium hydroxide. This lowers the pH to lessthan 10.3, causing an ethyl violet indictor to turn from clear topurple. By monitoring how much of the adsorbent has been converted, theanesthesiologist can determine how much time is available before theadsorbent must be changed. Indicator also allows decisions to be madebetween procedures as to whether adsorbent beds should be changed beforethe next procedure.

One problem with existing granular absorbents is that the indicatingchemistry may be a contaminant, and this contaminant is currently mixedin throughout all of the adsorbent. The US Navy uses calcium hydroxideCO₂ adsorbents for military rebreather diving, and reported an incidentwhere amine odors were observed with the use of color indicatinggranular adsorbents (https://www.ncbi.nlm.nih.gov/pubmed/8653065).

Methods have been proposed to put indicator not in the adsorbent, butrather in thin layers between the adsorbent and an outer transparentwall of the canister that holds the adsorbent (U.S. Pat. Nos. 4,326,514;5,109,838). This does not, however, address another issue with granularadsorbents. Improperly packed beds or beds that settle during shippingcan lead to gas channeling (Miller, R. D. et. al., Miller's Anesthesia,vol. 1. 2015, Elsevier, p. 788-790) and therefore a non-uniform reactionzone (FIG. 2), which makes it difficult to objectively determine whenthe granular bed is spent. Adsorbent canisters are therefore oftenpulled well before all of the adsorbent is utilized, to prevent thepossibility of patient exposure to excessive levels of carbon dioxidedue to early breakthrough. The use of indicating layers on the outsideof an adsorbent bed does not give information on potential gaschanneling and early breakthrough inside the bed.

Another problem with existing granular absorbent indicators is that thegradual color change from unreacted to reacted material makes itdifficult to discern the location of the reaction front.

As shown in FIG. 2, the front of color indicator can move less thanone-third the length of a granule filled canister from initialbreakthrough to final exhaustion. This does not give the best possibleresolution for consistently and accurately measuring the amount ofunreacted adsorbent. It would be better if the color indicator frontmoved across the entire canister length, from initial breakthrough tofinal exhaustion.

Another problem is that many indicators used with granular CO₂adsorbents revert back to their initial color after the end of aprocedure (U.S. Pat. No. 7,476,641). This can happen in the calciumhydroxide system employing sodium hydroxide because the sodium hydroxidethat is initially consumed in the reaction sequence—decreasing the pHand turning ethyl violet to purple—is slowly regenerated at the end ofthe reaction sequence, thereby increasing the pH and turning the ethylviolet back to clear. This makes it difficult to determine if partiallyused adsorbents beds have enough capacity to be used in anotherprocedure.

In summary, there is a need for an adsorbent cartridge that gives auniform and reproducible flow front with a sharply contrasting indicatorthat gives an accurate, objective and long lasting indication of theconsumption state of the adsorbent within the cartridge. This inventionaddresses this need and others.

SUMMARY

The present invention is an adsorbent cartridge comprised of layers ofadsorbent sheet with a color indicator system. The cartridge providesfor a uniform flow front and the indicator displays the degree ofconsumption of the adsorbent in an objective, accurate and long lastingmanner. This allows for maximum use of adsorbent in the cartridge beforeit is replaced. In one embodiment, windows (openings) are cut in anoutermost layer of the adsorbent cartridge and color indicator is coatedon an area on the layer beneath the outermost layer, so that it isvisible through the window.

The absorbent cartridges described herein also allow for use of verylittle indicator dye compared to a granule bed (e.g., 1/100 to 1/100,000less color indicator on a weight basis compared to a granule bed with acolor indicator).

Accordingly, the present invention provides an adsorbent cartridge forremoving gaseous contaminants, comprising layers of one or moreself-supporting adsorbent sheets mechanically spaced to provide gas flowchannels between the layers from one end of the cartridge to the other,wherein the cartridge further comprises a color indicator for visuallyindicating consumption of the adsorbent to an external observer, whereinat least one area of color indicator is visually exposed to an externalobserver while the cartridge is in use.

In some embodiments, the color indicator is visually exposed by windowscut into the side of the cartridge. In another embodiment, windows arecut in an outermost layer of the adsorbent cartridge. In someembodiments, a very thin color indicator layer with an area that islarger than the window area is placed between the window layer and thelayer beneath the outermost layer, so that it is visible through thewindow.

In another embodiment, windows are cut in an outermost layer of theadsorbent cartridge and the window space is at least partially filledwith a plug of indicating material that is the same areal dimensions asthe plug.

In any embodiment using windows, a transparent layer may be placed overthe outermost layer and its windows so that the indicator below thewindow can be seen without the gas in the cartridge escaping.

In another embodiment, stripes or other discrete geometric patterns canbe coated onto the surface of the outer adsorbent layer of thecartridge.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1(a) depicts a three-quarter perspective view of an adsorptioncartridge of the present invention where the cartridge is cylindricaland the sheets are spiral.

FIG. 1(b) depicts a cross-section top view of the adsorption canister ofFIG. 1(a) where the sheets inside the canister have a spiralconfiguration.

FIG. 1(c) depicts an enlargement of the circular area of thecross-section shown in FIG. 1(b) showing the sheets separated by aseparating means.

FIG. 1(d) depicts a cross-section view of an adsorption sheet of thepresent invention where the sheet is formed with adsorbent particlesconnected by polymer within.

FIG. 1(e) depicts a cross-section view of an adsorption sheet of thepresent invention where the sheet of FIG. 1(d) is surrounded by an outermembrane.

FIG. 1(f) depicts a cross-section view of an adsorption sheet of thepresent invention where adsorbent material is attached to an internalscreen and outer membranes are attached to the adsorbent particles.

FIG. 1(g) depicts a cross-section view of an adsorption sheet of thepresent invention where outer membranes are attached to an internalscreen and the interstices in the screen contain adsorbent material.

FIGS. 1(h) through 1(k) depict three-quarter elevation views of a methodfor forming the sheet of FIG. 1(g).

FIG. 1(l) depicts a scanning electron micrograph (SEM), enlarged 5,000times, of a cross section of an adsorbent sheet of the present inventionwere the adsorbent powder is formed into a microporous sheet bythermally induced phase separation of polyethylene.

FIG. 1(m) depicts a three-quarter top elevation view of an adsorbentsheet for use in the present invention, in which separating ribs havebeen molded on one side of the sheet out of the adsorbent itself. FIG.1(n) depicts a cross-section view of the adsorbent sheet shown in FIG.1(m).

FIG. 1(o) depicts a three-quarter top elevation view of anotherembodiment of an adsorbent sheet for use in the present invention, inwhich separating ribs have been molded in an angular fashion on one sideof the adsorbent sheet.

FIG. 1(p) depicts a three-quarter side elevation view of still anotherembodiment of an adsorbent sheet for use in the present invention, inwhich separating ribs have been molded in an angular fashion on bothsides of the adsorbent sheet.

FIG. 1(q) depicts a detailed view of the adsorbent sheet illustrated inFIG. 1(p).

FIG. 2 depicts channeling of a color indicator in a granule-basedadsorbent system.

FIG. 3 depicts an adsorbent cartridge having ribs molded from theadsorbent sheet which provide gas flow channels when wound.

FIG. 3a depicts an adsorbent cartridge having ribs molded from theadsorbent sheet which provide flow channels when stacked.

FIG. 4 depicts an adsorbent cartridge having a wound adsorbent sheethaving windows cut in the outermost layer for viewing a color indicatorapplied to the layer beneath the outermost layer of the cartridge.

FIG. 5(a)-(b) depict an adsorbent cartridge having a wound adsorbentsheet having windows cut in the outermost layer where ethyl violetindicator has been applied to the layer beneath the outermost layer ofthe cartridge. The indicator is initially purple (FIG. 5(a)), but turnsclear once in contacts the sodium hydroxide in the cartridge (FIG.5(b)).

FIG. 6 depicts an adsorbent cartridge having a wound adsorbent sheet, towhich has been applied ethyl violet indicator, after exposure to carbondioxide after 3, 4, 6, and 12.6 hours.

FIG. 7 depicts an adsorbent cartridge having a wound adsorbent sheethaving windows cut in the outermost layer where ethyl violet indicatorhas been applied to the layer beneath the outermost layer of thecartridge, after exposure to carbon dioxide 1, 5, 8 13.3, and 14.8hours.

FIG. 8 depicts the adsorbent cartridge from FIG. 7 at 0, 22, 42, and 75hours after the test, showing that the color change does not quicklyrevert.

DETAILED DESCRIPTION

The present invention is an adsorbent cartridge comprised of layers ofadsorbent sheet with a color indicator system. The cartridge providesfor uniform flow front (see FIG. 6) unlike a granule adsorbent front(see FIG. 2). Because the flow front is uniform, a color indicator asused in the present application can display the degree of consumption ofthe adsorbent in an objective, accurate and long lasting manner. Thisallows for maximum use of adsorbent in the cartridge before it isreplaced.

Embodiments of the present application may be particularly useful foruse in the administration of anesthesia, where it is desirable toconsume as much of the CO₂ adsorbent as possible while not exposing thepatient to excessive CO₂ levels that could be caused by gas channelingand premature breakthrough. Further, certain embodiments having discreteareas of color indicator allow the amount of indicator to be minimized,thereby increasing the safety of the instant adsorbent cartridge byminimizing any contamination from the indicator itself. The presentinvention may also be used as a means to reduce CO₂ and give visualindication of adsorbent consumption in other devices, such as underwater breathing apparatus.

As the mechanism for removing CO₂ from a gas or inhaled air is dependenton the particular material chosen, the use of the work ‘adsorption’ inthis specification is meant to include adsorption, absorption,chemisorption and so forth.

Accordingly, the present application provides, inter alia, an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide or lithium hydroxide, wherein the cartridgefurther comprises a color indicator for visually indicating consumptionof the adsorbent to an external observer, wherein at least one area ofcolor indicator is visually exposed to an external observer while thecartridge is in use.

In another embodiment, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising astack of self-supporting adsorbent sheets mechanically spaced to providegas flow channels between the layers from one end of the cartridge tothe other, wherein the sheet is formed from a mixture comprising polymerand an adsorbent material comprising calcium hydroxide or lithiumhydroxide, wherein the cartridge further comprises a color indicator forvisually indicating consumption of the adsorbent to an externalobserver, wherein at least one area of color indicator is visuallyexposed to an external observer while the cartridge is in use.

In another embodiment, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide or lithium hydroxide, wherein the cartridgefurther comprises a color indicator for visually indicating consumptionof the adsorbent to an external observer, wherein at least one area ofcolor indicator is visually exposed to an external observer while thecartridge is in use, wherein the total surface area of the visuallyexposed areas of color indicator is equal to or less than the totalsurface area of the outermost layer of the cartridge.

In another embodiment, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising astack of self-supporting adsorbent sheets mechanically spaced to providegas flow channels between the layers from one end of the cartridge tothe other, wherein the sheet is formed from a mixture comprising polymerand an adsorbent material comprising calcium hydroxide or lithiumhydroxide, wherein the cartridge further comprises a color indicator forvisually indicating consumption of the adsorbent to an externalobserver, wherein at least one area of color indicator is visuallyexposed to an external observer while the cartridge is in use, whereinthe total surface area of the visually exposed areas of color indicatoris equal to or less than the total surface area of the outermost layerof the cartridge.

In another embodiment, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide or lithium hydroxide, wherein the cartridgefurther comprises a color indicator for visually indicating consumptionof the adsorbent to an external observer, wherein at least one area ofcolor indicator is visually exposed to an external observer while thecartridge is in use, wherein the total surface area of all colorindicator in the cartridge is equal to or less than the total surfacearea of the outermost layer of the cartridge; and wherein the totalsurface area of the visually exposed areas of color indicator is equalto or less than the total surface area of all color indicator in thecartridge.

In another embodiment, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants, comprising astack of self-supporting adsorbent sheets mechanically spaced to providegas flow channels between the layers from one end of the cartridge tothe other, wherein the sheet is formed from a mixture comprising polymerand an adsorbent material comprising calcium hydroxide or lithiumhydroxide, wherein the cartridge further comprises a color indicator forvisually indicating consumption of the adsorbent to an externalobserver, wherein at least one area of color indicator is visuallyexposed to an external observer while the cartridge is in use, whereinthe total surface area of all color indicator in the cartridge is equalto or less than the total surface area of the outermost layer of thecartridge; and wherein the total surface area of the visually exposedareas of color indicator is equal to or less than the total surface areaof all color indicator in the cartridge.

As used herein, the “outermost layer” in the context of the spirallywound adsorbent cartridge refers to the final wound layer of thecartridge. The “outermost layer” in the context of the stacked adsorbentcartridge refers to the top or bottom sheet of the stack of adsorbentsheets.

As used herein, “self-supporting” adsorbent sheet means that the sheetdoes not require any external reinforcement for support after beingwound or stacked.

As used herein, the “color indicator” refers to a dye that changes colorwhen the absorbent is reacted. In the case of calcium hydroxide, thisthe color change occurs because of the decrease in pH due to theconversion of calcium hydroxide to calcium carbonate, as well as theshort term consumption of sodium hydroxide. For example, for ethylviolet indicator, the pH changes to less than 10.3, causing the ethylviolet indictor to turn from clear to purple.

As used herein, “inner side of the adsorbent sheet” in the context of aspirally wound adsorbent cartridge means the side of adsorbent sheetthat faces towards the core of wound roll.

As used herein, “the outer side of the adsorbent sheet” in the contextof a spirally wound adsorbent cartridge means the side of the adsorbentsheet that faces away from the core of the wound roll.

As used herein, “total surface area of all color indicator in thecartridge” means the total surface area of all applied color indicatorin the cartridge, whether applied directly to a layer of the cartridge,to an indicator layer, or to a plug of material comprising colorindicator.

As used herein, “visually exposed areas of color indicator” means theareas of color indicator which are visible to an external observerbecause they are applied to the outermost layer of the cartridge orwhich are exposed due to windows cut in the outermost layer.

Embodiments below may be combined in any combination with the precedingembodiments.

In some embodiments, the cartridge is for use in an anesthesia breathingcircuit. In some embodiments, the multiple layers are mechanicallyspaced by parallel, longitudinal ribs molded out of the sheet. As usedherein, “parallel, longitudinal ribs” means that the ribs run parallelto the direction of air flow, thereby mechanically separating the sheetlayers and providing gas flow channels. In some embodiments, the layersare mechanically spaced by additional spacer material. In someembodiments, the adsorbent material comprises calcium hydroxide. In someembodiments, the adsorbent material comprises lithium hydroxide. In someembodiments, the adsorbent material comprises calcium hydroxide, sodiumhydroxide, and potassium hydroxide. In some embodiments, the adsorbentmaterial comprises calcium hydroxide and sodium hydroxide. In someembodiments, the adsorbent material further comprises sodium hydroxide,potassium hydroxide, calcium chloride, or lithium hydroxide. In someembodiments, the cartridge further comprising a transparent filmcovering the outermost layer of the cartridge. In some embodiments, thetotal surface area of visibly exposed areas of color indicator is 0.05%to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or0.5% to 5% of the surface area of the outermost layer. In someembodiments, the total surface area of color indicator in the cartridgeis 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%,0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05%to 1%, or 0.5% to 5% of the surface area of the outermost layer.

In some embodiments, the polymer comprises 0.25% to 10%, 0.25% to 9%,0.25% to 8%, 0.25% to 7%, 0.25% to 6%, 0.25% to 5%, 0.25% to 4%, 0.25%to 3%, 0.25% to 2%, or 0.25% to 1% by weight of said sheet. In someembodiments, the polymer comprises 0.5% to 1%, 0.5% to 2%, 0.5% to 3%,0.5% to 4%, 0.5% to 5%, 0.5% to 6%, 0.5% to 7%, 0.5% to 8%, 0.5% to 9%,0.5% to 10%, 0.5% to 15%, or 0.5% to 20% by volume of the adsorbentmaterial which is formed into the sheet. In some embodiments, thepolymer is polyethylene. In some embodiments, the polymer ishigh-density polyethylene or ultra high molecular weight polyethylene.In some embodiments, the adsorbent sheet is made by a thermally inducedphase separation process. In some embodiments, the polymer is apolyethylene binder. In some embodiments, the adsorbent sheet is made bya thermally induced phase separation process wherein the polymer ispolyethylene that comprises 0.25% to 10%, 0.25% to 9%, 0.25% to 8%,0.25% to 7%, 0.25% to 6%, 0.25% to 5%, 0.25% to 4%, 0.25% to 3%, 0.25%to 2%, or 0.25% to 1% by weight of said sheet.

In some embodiments, the ribbed adsorbent sheet is less than 0.10inches, 0.09 inches, less than 0.08 inches, less than 0.07 inches, lessthan 0.06 inches, less than 0.05 inches, less than 0.04 inches, or lessthan 0.03 inches in thickness, including the ribs. In some embodiments,the thickness of the sheet, excluding the ribs is from 0.01 to 0.07inches, or 0.01 to 0.08 inches. In some embodiments, the thickness ofthe ribs disposed on the sheet is from 0.01 to 0.04 inches. In someembodiments, the height of the ribs disposed on the sheet is from 0.005to 0.05 inches. In some embodiments, the height of the ribs disposed onthe sheet is from 0.005 to 0.08 inches.

The absorbent may be a single absorbent or a mixture of differentadsorbents. In some embodiments, the adsorbent includes, but is notlimited to, calcium hydroxide (Ca(OH)₂), lithium hydroxide (LiOH),calcium hydroxide mixed with a percentage of sodium and potassiumhydroxide, other CO₂ adsorbents and mixtures thereof. In someembodiments, the adsorbent (e.g., calcium hydroxide) is mixed with otheralkali metal hydroxides such as sodium hydroxide or potassium hydroxide.In some embodiments, the adsorbent particles form at least 75%, 80%,85%, 90%, 95%, 96%, 97%, 99%, or 99.5% by weight of said sheet. In someembodiments, the adsorbent particles form at least 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, or 75%, by volume of adsorbent material whichis formed into the sheet.

The following sections detail specific embodiments of the presentapplication. The embodiments in each individual paragraph can combinedin any combination.

Discrete Areas of Indicator Applied to a Layer of the Cartridge

In some embodiments, the color indicator is applied to one or morelayers of the cartridge solely on the outer side of the adsorbent sheet,wherein one or more discrete areas of color indicator are visible toexternal observer or are exposed visually to an external observerthrough windows cut into the outermost layer. In some embodiments, thecartridge is for use in an anesthesia breathing circuit. In someembodiments, the multiple layers are mechanically spaced by parallel,longitudinal ribs molded out of the sheet. In some embodiments, thelayers are mechanically spaced by additional spacer material. In someembodiments, the adsorbent material comprises calcium hydroxide. In someembodiments, the adsorbent material comprises lithium hydroxide. In someembodiments, the adsorbent material further comprises sodium hydroxide,potassium hydroxide, calcium chloride, or lithium hydroxide. In someembodiments, the cartridge further comprises a transparent film coveringthe outermost layer of the cartridge. In some embodiments, the colorindicator comprises ethyl violet, Titan yellow, Kenazol yellow,activated alumina with thymol blue, or o-cresolpthalein. In someembodiments, the color indicator comprises ethyl violet. In someembodiments, the total surface area of visibly exposed areas of colorindicator is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer. In some embodiments, the total surface area of color indicator inthe cartridge is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer.

In some embodiments, the adsorbent cartridge comprises 1/100 to1/100,000 less color indicator on a weight basis compared to a granulebed with a color indicator.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein a color indicator for visuallyindicating consumption of the adsorbent to an external observer isapplied to one or more layers of the cartridge solely on the outer sideof the adsorbent sheet, wherein one or more discrete areas of colorindicator are visible to external observer or are exposed visually to anexternal observer through windows cut into the outermost layer, whereinthe total surface area of all color indicator in the cartridge is equalto or less than the total surface area of the outermost layer of thecartridge; and wherein the total surface area of the visually exposedareas of color indicator is equal to or less than the total surface areaof all color indicator in the cartridge. In some embodiments, the totalsurface area of visibly exposed areas of color indicator is 0.05% to40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or0.5% to 5% of the surface area of the outermost layer. In someembodiments, the total surface area of color indicator in the cartridgeis 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%,0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05%to 1%, or 0.5% to 5% of the surface area of the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein an ethyl violet color indicatorfor visually indicating consumption of the adsorbent to an externalobserver is applied to one or more layers of the cartridge solely on theouter side of the adsorbent sheet, wherein one or more discrete areas ofcolor indicator are visible to external observer or are exposed visuallyto an external observer through windows cut into the outermost layer,wherein the total surface area of all color indicator in the cartridgeis equal to or less than the total surface area of the outermost layerof the cartridge; and wherein the total surface area of the visuallyexposed areas of color indicator is equal to or less than the totalsurface area of all color indicator in the cartridge. In someembodiments, the total surface area of visibly exposed areas of colorindicator is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer. In some embodiments, the total surface area of color indicator inthe cartridge is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein a color indicator for visually indicatingconsumption of the adsorbent to an external observer is applied to oneor more layers of the cartridge solely on the outer side of theadsorbent sheet, wherein one or more discrete areas of color indicatorare visible to external observer or are exposed visually to an externalobserver through windows cut into the outermost layer, wherein the totalsurface area of all color indicator in the cartridge is equal to or lessthan the total surface area of the outermost layer of the cartridge andwherein the total surface area of the visually exposed areas of colorindicator is equal to or less than the total surface area of all colorindicator in the cartridge. In some embodiments, the total surface areaof visibly exposed areas of color indicator is 0.05% to 40%, 0.05% to30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% ofthe surface area of the outermost layer. In some embodiments, the totalsurface area of color indicator in the cartridge is 0.05% to 40%, 0.05%to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% ofthe surface area of the outermost layer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide, wherein an ethyl violet color indicator for visuallyindicating consumption of the adsorbent to an external observer isapplied to one or more layers of the cartridge solely on the outer sideof the adsorbent sheet, wherein one or more discrete areas of colorindicator are visible to external observer or are exposed visually to anexternal observer through windows cut into the outermost layer, whereinthe total surface area of all color indicator in the cartridge is equalto or less than the total surface area of the outermost layer of thecartridge and wherein the total surface area of the visually exposedareas of color indicator is equal to or less than the total surface areaof all color indicator in the cartridge. In some embodiments, the totalsurface area of visibly exposed areas of color indicator is 0.05% to40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or0.5% to 5% of the surface area of the outermost layer. In someembodiments, the total surface area of color indicator in the cartridgeis 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%,0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05%to 1%, or 0.5% to 5% of the surface area of the outermost layer.

Discrete Areas of Color Indicator Applied to the Outermost Layer of theCartridge

In some embodiments, the color indicator can be applied to one or morediscrete areas of the outermost layer of the cartridge. The colorindicator can be applied either directly to the outermost layer or aspart of a coating containing another substances (e.g., a polymerbinder). Hence, in some embodiments, each of the discrete areas of thecolor indicator are applied to the outermost layer of the cartridge. Insome embodiments, the color indicator comprises ethyl violet, Titanyellow, Kenazol yellow, activated alumina with thymol blue, oro-cresolpthalein. In some embodiments, the cartridge further comprisinga transparent film covering the outermost layer of the cartridge. Insome embodiments, each discrete area of color indicator is 0.05% to 50%of the surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein color indicator for visuallyindicating consumption of the adsorbent to an external observer isapplied to one or more discrete areas of the outermost layer of thecartridge, wherein the total surface area of the visually exposed areasof color indicator is equal to or less than the total surface area ofthe outermost layer of the cartridge. In some embodiments of theprevious embodiment, the color indicator comprises ethyl violet, Titanyellow, Kenazol yellow, activated alumina with thymol blue, oro-cresolpthalein. In some embodiments of the previous embodiment, thecolor indicator comprises ethyl violet. In some embodiments of any ofthe previous embodiments of this paragraph, at least one of the discreteareas of color indicator is positioned at the end of the cartridge fromwhich the gas exits. In some embodiments of any of the previousembodiments of this paragraph, the discrete areas of color indicator arepositioned at various points in the direction of gas flow so consumptionof the adsorbent material can be assessed. In some embodiments, thecartridge further comprising a transparent film covering the outermostlayer of the cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein ethyl violet color indicator forvisually indicating consumption of the adsorbent to an external observeris applied to one or more discrete areas of the outermost layer of thecartridge, wherein the total surface area of the visually exposed areasof color indicator is equal to or less than the total surface area ofthe outermost layer of the cartridge. In some embodiments of theprevious embodiment, at least one of the discrete areas of colorindicator is positioned at the end of the cartridge from which the gasexits. In some embodiments of any of the previous embodiments of thisparagraph, the discrete areas of color indicator are positioned atvarious points in the direction of gas flow so consumption of theadsorbent material can be assessed. In some embodiments, the cartridgefurther comprising a transparent film covering the outermost layer ofthe cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide, wherein color indicator for visually indicating consumptionof the adsorbent to an external observer is applied to one or morediscrete areas of the outermost layer of the cartridge, wherein thetotal surface area of the visually exposed areas of color indicator isequal to or less than the total surface area of the outermost layer ofthe cartridge. In some embodiments of the previous embodiment, the colorindicator comprises ethyl violet, Titan yellow, Kenazol yellow,activated alumina with thymol blue, or o-cresolpthalein. In someembodiments of the previous embodiment, the color indicator comprisesethyl violet. In some embodiments of any of the previous embodiments ofthis paragraph, at least one of the discrete areas of color indicator ispositioned at the end of the cartridge from which the gas exits. In someembodiments of any of the previous embodiments of this paragraph, thediscrete areas of color indicator are positioned at various points inthe direction of gas flow so consumption of the adsorbent material canbe assessed. In some embodiments, the cartridge further comprising atransparent film covering the outermost layer of the cartridge. In someembodiments, each discrete area of color indicator is 0.05% to 50% ofthe surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide, wherein ethyl violet color indicator for visually indicatingconsumption of the adsorbent to an external observer is applied to oneor more discrete areas of the outermost layer of the cartridge, whereinthe total surface area of the visually exposed areas of color indicatoris equal to or less than the total surface area of the outermost layerof the cartridge. In some embodiments of the previous embodiment, atleast one of the discrete areas of color indicator is positioned at theend of the cartridge from which the gas exits. In some embodiments ofany of the previous embodiments of this paragraph, the discrete areas ofcolor indicator are positioned at various points in the direction of gasflow so consumption of the adsorbent material can be assessed. In someembodiments of any of the previous embodiments of this paragraph, thecartridge further comprising a transparent film covering the outermostlayer of the cartridge. In some embodiments of any of the previousembodiments of this paragraph, each discrete area of color indicator is0.05% to 50% of the surface area of the outermost layer. In someembodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

Color Indicator Applied to Layer Beneath the Outermost Layer of theCartridge

Instead of applying the color indicator to the outermost layer, windowscan be cut into the outermost layer of the adsorbent cartridge. Colorindicator can then be applied directly or as a coating (e.g., withanother material like a binder or polymer) to the layer beneath theoutermost layer of the cartridge. In the case of spirally woundcartridge, this would be the layer (or wrap) of the adsorbent sheetunder the outermost layer. In the case of the stacked cartridge, thiswould be the adsorbent sheet immediately under the outermost adsorbentsheet in the stack. The size of the area(s) of color indicator may belarger or smaller than the size of the window, but should be viewablethrough the window.

Accordingly, in some embodiments, in some embodiments, the colorindicator can be applied to one or more discrete areas of the layerbeneath the outermost layer of the cartridge. The color indicator can beapplied either directly to the layer beneath the outermost layer or aspart of a coating containing another substances (e.g., a polymerbinder). Hence, in some embodiments, each of the discrete areas of thecolor indicator are applied to the layer beneath the outermost layer ofthe cartridge. In some embodiments, the color indicator comprises ethylviolet, Titan yellow, Kenazol yellow, activated alumina with thymolblue, or o-cresolpthalein. In some embodiments, the color indicator isethyl violet. In some embodiments, the cartridge further comprises atransparent film covering the outermost layer of the cartridge. In someembodiments, each discrete area of color indicator is 0.05% to 50% ofthe surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein color indicator for visuallyindicating consumption of the adsorbent to an external observer isapplied to one or more discrete areas of the layer beneath the outermostlayer of the cartridge and the one or more discrete areas of the colorindicator are exposed visually to the external observer by windows cutin the outermost layer of the cartridge, wherein the total surface areaof all areas of color indicator is equal to or less than the totalsurface area of the outermost layer of the cartridge. In someembodiments of the previous embodiment, the color indicator comprisesethyl violet, Titan yellow, Kenazol yellow, activated alumina withthymol blue, or o-cresolpthalein. In some embodiments of the previousembodiment, the color indicator comprises ethyl violet. In someembodiments of any of the previous embodiments of this paragraph, atleast one of the discrete areas of color indicator is positioned at theend of the cartridge from which the gas exits. In some embodiments ofany of the previous embodiments of this paragraph, the discrete areas ofcolor indicator are positioned at various points in the direction of gasflow so consumption of the adsorbent material can be assessed. In someembodiments, the cartridge further comprising a transparent filmcovering the outermost layer of the cartridge. In some embodiments, eachdiscrete area of color indicator is 0.05% to 50% of the surface area ofthe outermost layer. In some embodiments, each discrete area of colorindicator is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants, comprising aself-supporting adsorbent sheet wound into a roll to form multiplelayers mechanically spaced to provide gas flow channels between thelayers from one end of the cartridge to the other, wherein the sheet isformed from a mixture comprising polymer and an adsorbent materialcomprising calcium hydroxide, wherein ethyl violet color indicator forvisually indicating consumption of the adsorbent to an external observeris applied to one or more discrete areas of the layer beneath theoutermost layer of the cartridge and the one or more discrete areas ofthe color indicator are exposed visually to the external observer bywindows cut in the outermost layer of the cartridge, wherein the totalsurface area of all areas of color indicator is equal to or less thanthe total surface area of the outermost layer of the cartridge. In someembodiments of the previous embodiment, at least one of the discreteareas of color indicator is positioned at the end of the cartridge fromwhich the gas exits. In some embodiments of any of the previousembodiments of this paragraph, the discrete areas of color indicator arepositioned at various points in the direction of gas flow so consumptionof the adsorbent material can be assessed. In some embodiments, thecartridge further comprising a transparent film covering the outermostlayer of the cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide, wherein color indicator for visually indicating consumptionof the adsorbent to an external observer is applied to one or morediscrete areas of the layer beneath the outermost layer of the cartridgeand the one or more discrete areas of the color indicator are exposedvisually to the external observer by windows cut in the outermost layerof the cartridge, wherein the total surface area of all areas of colorindicator is equal to or less than the total surface area of theoutermost layer of the cartridge. In some embodiments of the previousembodiment, the color indicator comprises ethyl violet, Titan yellow,Kenazol yellow, activated alumina with thymol blue, or o-cresolpthalein.In some embodiments of the previous embodiment, the color indicatorcomprises ethyl violet. In some embodiments of any of the previousembodiments of this paragraph, at least one of the discrete areas ofcolor indicator is positioned at the end of the cartridge from which thegas exits. In some embodiments of any of the previous embodiments ofthis paragraph, the discrete areas of color indicator are positioned atvarious points in the direction of gas flow so consumption of theadsorbent material can be assessed. In some embodiments, the cartridgefurther comprising a transparent film covering the outermost layer ofthe cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the present application provides an adsorbentcartridge for removing gaseous carbon dioxide contaminants for use in ananesthesia breathing circuit, comprising an adsorbent sheet wound into aroll to form multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide, wherein ethyl violet color indicator for visually indicatingconsumption of the adsorbent to an external observer is applied to oneor more discrete areas of the layer beneath the outermost layer of thecartridge and the one or more discrete areas of the color indicator areexposed visually to the external observer by windows cut in theoutermost layer of the cartridge, wherein the total surface area of allareas of color indicator is equal to or less than the total surface areaof the outermost layer of the cartridge. In some embodiments of theprevious embodiment, at least one of the discrete areas of colorindicator is positioned at the end of the cartridge from which the gasexits. In some embodiments of any of the previous embodiments of thisparagraph, the discrete areas of color indicator are positioned atvarious points in the direction of gas flow so consumption of theadsorbent material can be assessed. In some embodiments of any of theprevious embodiments of this paragraph, the cartridge further comprisinga transparent film covering the outermost layer of the cartridge. Insome embodiments of any of the previous embodiments of this paragraph,each discrete area of color indicator is 0.05% to 50% of the surfacearea of the outermost layer. In some embodiments, each discrete area ofcolor indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%,0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of theoutermost layer.

In some embodiments, the cartridge can be used in conjunction with aflow cone for improving uniformity of flow, which is placed at the gasinlet and/or outlet end of the cartridge. For example, appropriate flowcones are described in U.S. Pat. No. 7,326,280, which is incorporatedherein by reference in its entirety.

Use of an Indicator Layer

In another configuration, windows can be cut into the outermost layer ofthe adsorbent cartridge as above. In some embodiments, a single windowmay be cut, while in other embodiments, multiple windows can be cut.However, instead of applying the color indicator to a particular layerof the cartridge itself, an indicator layer comprising a color indicatorcan then be sandwiched between the outermost layer and a layerimmediately beneath the outermost layer. The indicator layer should bethin to minimize any bulging of the adsorbent cartridge. The indicatorlayer may have the color indicator applied to part or the entire surfaceof the indicator surface, on one side or both sides of the indicatorlayer. In some embodiments, the color indicator may be patterned indiscrete areas of the indicator layer rather than in a continuous area.If coated on one side, the color indicator should be positioned on theside facing the window so that the color change can be viewed throughthe window by an external observer. The indicator layer may be a film orother thin material coated with the color indicator. If using discreteareas of color indicator on the indicator layer, the size of thediscrete area of color indicator may be larger or smaller than the sizeof the window, but should be viewable through the window. In someembodiments, a single indicator layer may be used, but positioned so thearea of color indicator is visible through the window(s) in theoutermost layer. In some embodiments, separate thin indicator layers(patches) can be used for each window cut into the outermost layer.

Accordingly, in some embodiments, the color indicator comprises part ofan indicator layer sandwiched between the outermost layer and the layerbeneath the outermost layer of the cartridge, wherein each discrete areaof color indicator is exposed by a window cut in the outermost layer ofthe cartridge. In some embodiments, the indicator is 30 mils or less inthickness. In some embodiments, the indicator layer is 20 mils or lessin thickness. In some embodiments, the indicator layer is 10 mils orless in thickness. In some embodiments, the indicator layer is formedfrom a mixture comprising calcium hydroxide, sodium hydroxide, and apolymer, to which the color indicator has been applied. In someembodiments, the color indicator is ethyl violet. In some embodiments,the color indicator comprises Titan yellow, Kenazol yellow, activatedalumina with thymol blue, or o-cresolpthalein. In some embodiments, theadsorbent material comprises lithium hydroxide. In some embodiments, thecartridge further comprising a transparent film covering the outermostlayer of the cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

The cartridge can have a single window and a single indicator layercomprising an area of color indicator is positioned so that the area ofcolor is positioned so that the area of color indicator is vieweablethrough the window. Accordingly, in some embodiments, the cartridge hasa single window, wherein the indicator layer has a single discrete areaof the color indicator positioned to center on the window in theoutermost layer of the cartridge. In some embodiments, the indicatorlayer is formed from a mixture of calcium hydroxide, sodium hydroxide,and a polymer, to which the discrete area of color indicator has beenapplied. In some embodiments, the color indicator is ethyl violet. Insome embodiments, the adsorbent material comprises lithium hydroxide. Insome embodiments, the cartridge further comprising a transparent filmcovering the outermost layer of the cartridge. In some embodiments, thecolor indicator is applied only to part of the indicator layer. In someembodiments, the color indicator is applied to the entire indicatorlayer (e.g, the indicator layer is used as patch under the window). Insome embodiments, each discrete area of color indicator is 0.05% to 50%of the surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

In a further embodiment, the indicator layer may be patterned withdiscrete areas of color indicator rather than being completely coatedwith color indicator. If coated on one side of the indicator layer, thecolor indicator should be positioned on the side facing the window sothat the color change can be viewed through the window by an externalobserver. The indicator layer is then positioned such that the areas ofcolor indicator can be viewed through the windows cut in the outermostlayer of the adsorbent.

Hence, in some embodiments, the cartridge has multiple windows, whereinthe indicator layer has multiple discrete areas of the color indicatorpositioned to center on the windows in the outermost layer of thecartridge. In some embodiments, the indicator layer is formed from amixture of calcium hydroxide, sodium hydroxide, and a polymer, to whichthe discrete areas of color indicator have been applied. In someembodiments, the color indicator is ethyl violet. In some embodiments,the adsorbent material comprises lithium hydroxide. In some embodiments,the cartridge further comprising a transparent film covering theoutermost layer of the cartridge. In some embodiments, each discretearea of color indicator is 0.05% to 50% of the surface area of theoutermost layer. In some embodiments, each discrete area of colorindicator is 0.05% to 40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%,0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05%to 2%, 0.05% to 1%, or 0.5% to 5% of the surface area of the outermostlayer.

In another embodiment, the indicator layer can be a strip which to whichthe color indicator is applied. The strip can be placed longitudallyunder the outermost layer of the adsorbent cartridge. One or morewindows can then be cut into the outermost layer above the strip,allowing discrete areas of color indicator to be viewed through thewindow(s).

In another embodiment, the indicator layer can be a film or strippositioned on the outermost layer of the cartridge over a window cutinto the outermost layer of the cartridge.

Accordingly, in some embodiments, the cartridge has multiple windows,wherein the indicator layer is a strip positioned such that the areaexposed by each window is covered by said strip, thereby exposing thecolor indicator to said external observer. In some embodiments, thestrip is formed from a mixture of calcium hydroxide, sodium hydroxide,and a polymer, to which the color indicator has been applied. In someembodiments, the color indicator is ethyl violet. In some embodiments,the adsorbent material comprises lithium hydroxide.

In yet another embodiment, separate thin indicator layers (patches) canbe used for each window cut into the outermost layer, rather than asingle strip or indicator layer. The color indicator can be applied toeach patch and then positioned beneath each window, such that the areaof color indicator is viewable through the window cut in the outermostlayer.

Accordingly, in some embodiments, the cartridge has multiple windows,wherein a separate indicator layer is utilized for each window. In someembodiments, the indicator layer is formed from a mixture of calciumhydroxide, sodium hydroxide, and a polymer, to which the discrete areasof color indicator have been applied. In some embodiments, the colorindicator is ethyl violet. In some embodiments, the adsorbent materialcomprises lithium hydroxide. In some embodiments, the cartridge furthercomprising a transparent film covering the outermost layer of thecartridge. In some embodiments, each discrete area of color indicator is0.05% to 50% of the surface area of the outermost layer. In someembodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants for use in an anesthesiabreathing circuit, comprising an adsorbent sheet wound into a roll toform multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising lithiumhydroxide; wherein the color indicator for visually indicatingconsumption of the adsorbent to an external observer is applied to anindicator layer sandwiched between the outermost layer and the layerbeneath the outermost layer, wherein one or more discrete areas of colorindicator are exposed visually to external observer through windows cutinto the outermost layer; wherein the total surface area of all colorindicator in the cartridge is equal to or less than the total surfacearea of the outermost layer of the cartridge. In some embodiments of theprevious embodiment, the indicator layer is a sheet formed from amixture comprising calcium hydroxide, sodium hydroxide, and a polymer,to which the color indicator is applied, wherein the color indicator isethyl violet. In some embodiments of either of the previous twoembodiments, the indicator layer is 10 mils or less in thickness (oralternatively, 20 mils or less in thickness, or alternatively, 30 milsor less). In some of any of the previous three embodiments, thecartridge has a single window in the outermost layer of the cartridge,wherein the indicator layer partially or completely covers the layerbeneath the outermost layer of the cartridge, but wherein the indicatorlayer has a single discrete area of the color indicator positioned tocenter on the window in the outermost layer of the cartridge. In someembodiments of any of the previous three embodiments, the cartridge hasmultiple windows, wherein the indicator layer partially or completelycovers the layer beneath the outermost layer of the cartridge, but theindicator layer has multiple discrete areas of the color indicatorpositioned to center on the windows in the outermost layer of thecartridge. In some embodiments of any of the previous three embodiments,the cartridge has one or more windows, the indicator layer partially orcompletely covers the layer beneath the outermost layer of thecartridge, and the color indicator is applied to the entire indicatorlayer, wherein the only areas of color indicator visible to the externalobserver are through each window. In some embodiments of any of theprevious three embodiments, the cartridge has multiple windows, whereinthe indicator layer is a strip positioned such that the area exposed byeach window is covered by said strip, thereby exposing the colorindicator to said external observer. In some embodiments of any of theprevious three embodiments, the cartridge has multiple windows, whereina separate indicator layer is utilized for each window. In someembodiments of any of the previous embodiments of this paragraph, thecartridge further comprising a transparent film covering the outermostlayer of the cartridge. In some embodiments of any of the previousembodiments of this paragraph, at least one of the discrete areas ofcolor indicator is positioned at the end of the cartridge from which thegas exits. In some embodiments of any of the previous embodiments ofthis paragraph, the discrete areas of color indicator are positioned atvarious points in the direction of gas flow so consumption of theadsorbent material can be assessed. In some embodiments of any of theprevious embodiments of this paragraph, the indicator layer completelycovers the layer beneath the outermost layer of the cartridge. In someembodiments of any of the previous embodiments of this paragraph, theindicator layer partially covers the layer beneath the outermost layerof the cartridge. In some embodiments, the cartridge further comprisinga transparent film covering the outermost layer of the cartridge. Insome embodiments, each discrete area of color indicator is 0.05% to 50%of the surface area of the outermost layer. In some embodiments, thetotal surface area of all color indicator in the cartridge is 0.05% to40%, 0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to10%, 0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or0.5% to 5% of the surface area of the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants for use in an anesthesiabreathing circuit, comprising an adsorbent sheet wound into a roll toform multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide; wherein the color indicator for visually indicatingconsumption of the adsorbent to an external observer is applied to anindicator layer sandwiched between the outermost layer and the layerbeneath the outermost layer, wherein one or more discrete areas of colorindicator are exposed visually to external observer through windows cutinto the outermost layer; wherein the total surface area of all colorindicator in the cartridge is equal to or less than the total surfacearea of the outermost layer of the cartridge. In some embodiments of theprevious embodiment, the indicator layer is a sheet formed from amixture comprising calcium hydroxide, sodium hydroxide, and a polymer,to which the color indicator is applied, wherein the color indicator isethyl violet. In some embodiments of the previous embodiment, theindicator layer is a sheet formed from a mixture comprising calciumhydroxide, sodium hydroxide, and a polymer, to which the color indicatoris applied, wherein the color indicator is ethyl violet. In someembodiments of either of the previous two embodiments, the indicatorlayer is 10 mils or less in thickness (or alternatively, 20 mils or lessin thickness, or alternatively, 30 mils or less in thickness). In someof any of the previous three embodiments, the cartridge has a singlewindow in the outermost layer of the cartridge, wherein the indicatorlayer partially or completely covers the layer beneath the outermostlayer of the cartridge, but wherein the indicator layer has a singlediscrete area of the color indicator positioned to center on the windowin the outermost layer of the cartridge. In some embodiments of any ofthe previous three embodiments, the cartridge has multiple windows,wherein the indicator layer partially or completely covers the layerbeneath the outermost layer of the cartridge, but the indicator layerhas multiple discrete areas of the color indicator positioned to centeron the windows in the outermost layer of the cartridge. In someembodiments of any of the previous three embodiments, the cartridge hasmultiple windows, wherein the indicator layer is a strip positioned suchthat the area exposed by each window is covered by said strip, therebyexposing the color indicator to said external observer. In someembodiments of any of the previous three embodiments, the cartridge hasone or more windows, the indicator layer partially or completely coversthe layer beneath the outermost layer of the cartridge, and the colorindicator is applied to the entire indicator layer, wherein the onlyareas of color indicator visible to the external observer are thoseviewed through each window. In some embodiments of any of the previousthree embodiments, the cartridge has multiple windows, wherein aseparate indicator layer is utilized for each window. In any of theprevious embodiments of this paragraph, the cartridge further comprisinga transparent film covering the outermost layer of the cartridge. Insome embodiments of any of the previous embodiments of this paragraph,at least one of the discrete areas of color indicator is positioned atthe end of the cartridge from which the gas exits. In some embodimentsof any of the previous embodiments of this paragraph, the discrete areasof color indicator are positioned at various points in the direction ofgas flow so consumption of the adsorbent material can be assessed. Insome embodiments of any of the previous embodiments of this paragraph,the indicator layer completely covers the layer beneath the outermostlayer of the cartridge. In some embodiments of any of the previousembodiments of this paragraph, the indicator layer partially covers thelayer beneath the outermost layer of the cartridge. In some embodiments,the cartridge further comprising a transparent film covering theoutermost layer of the cartridge. In some embodiments, each discretearea of color indicator is 0.05% to 50% of the surface area of theoutermost layer. In some embodiments, the total surface area of allcolor indicator in the cartridge is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

Use of a Plug of Indicator

In some embodiments, the cartridge has one or more windows cut out ofthe outermost layer of the cartridge, wherein visibly exposed discreteareas of color indicator are formed by a plug of material comprising thecolor indicator which at least partially fills each window. In someembodiments of the previous embodiments, the plug has the same lengthand width dimensions as each window. In some embodiments, the indicatorlayer is formed from a mixture of calcium hydroxide, sodium hydroxide,and a polymer, to which the color indicator has been applied. In someembodiments, the color indicator is ethyl violet. In some embodiments,the color indicator comprises Titan yellow, Kenazol yellow, activatedalumina with thymol blue, or o-cresolpthalein. In some embodiments, theadsorbent material comprises lithium hydroxide. In some embodiments, theplug is 4 to 100 mils in thickness. In some embodiments, the cartridgefurther comprising a transparent film covering the outermost layer ofthe cartridge. In some embodiments, each discrete area of colorindicator is 0.05% to 50% of the surface area of the outermost layer. Insome embodiments, each discrete area of color indicator is 0.05% to 40%,0.05% to 30%, 0.05% to 25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%,0.05% to 5%, 0.05% to 4%, 0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5%to 5% of the surface area of the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants for use in an anesthesiabreathing circuit, comprising an adsorbent sheet wound into a roll toform multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising lithiumhydroxide; wherein the cartridge has one or more windows cut out of theoutermost layer of the cartridge, each window being at least partiallyfilled with a plug of material comprising a color indicator for visuallyindicating consumption of the adsorbent to an external observer. In someembodiments of the previous embodiment, the plug is formed from amixture comprising calcium hydroxide, sodium hydroxide, and a polymer,to which the color indicator is applied, wherein the color indicator isethyl violet. In some embodiments of either of the previous twoembodiments, the plug is 4 to 100 mils in thickness. In some embodimentsof any of the previous embodiments of this paragraph, the cartridgefurther comprising a transparent film covering the outermost layer ofthe cartridge. In some embodiments of any of the previous embodiments ofthis paragraph, at least one of the discrete areas of color indicator ispositioned at the end of the cartridge from which the gas exits. In someembodiments of any of the previous embodiments of this paragraph, thediscrete areas of color indicator are positioned at various points inthe direction of gas flow so consumption of the adsorbent material canbe assessed. In some embodiments, the cartridge further comprising atransparent film covering the outermost layer of the cartridge. In someembodiments, each discrete area of color indicator is 0.05% to 50% ofthe surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

In some embodiments, the application provides an adsorbent cartridge forremoving gaseous carbon dioxide contaminants for use in an anesthesiabreathing circuit, comprising an adsorbent sheet wound into a roll toform multiple layers which are mechanically spaced by parallel,longitudinal ribs molded out of the sheet to provide gas flow channelsbetween the layers, wherein the sheet is formed from a mixturecomprising polymer and an adsorbent material comprising calciumhydroxide; wherein the cartridge has one or more windows cut out of theoutermost layer of the cartridge, each window being at least partiallyfilled with a plug of material comprising a color indicator for visuallyindicating consumption of the adsorbent to an external observer. In someembodiments of the previous embodiment, the plug is formed from amixture comprising calcium hydroxide, sodium hydroxide, and a polymer,to which the color indicator is applied, wherein the color indicator isethyl violet. In some embodiments of either of the previous twoembodiments, the plug is 4 to 100 mils in thickness. In some embodimentsof any of the previous embodiments of this paragraph, the cartridgefurther comprising a transparent film covering the outermost layer ofthe cartridge. In some embodiments of any of the previous embodiments ofthis paragraph, at least one of the discrete areas of color indicator ispositioned at the end of the cartridge from which the gas exits. In someembodiments of any of the previous embodiments of this paragraph, thediscrete areas of color indicator are positioned at various points inthe direction of gas flow so consumption of the adsorbent material canbe assessed. In some embodiments, the cartridge further comprising atransparent film covering the outermost layer of the cartridge. In someembodiments, each discrete area of color indicator is 0.05% to 50% ofthe surface area of the outermost layer. In some embodiments, eachdiscrete area of color indicator is 0.05% to 40%, 0.05% to 30%, 0.05% to25%, 0.05% to 20%, 0.05% to 15%, 0.05% to 10%, 0.05% to 5%, 0.05% to 4%,0.05% to 3%, 0.05% to 2%, 0.05% to 1%, or 0.5% to 5% of the surface areaof the outermost layer.

Formation of Adsorbent Sheets and Cartridges

In certain embodiments, a wound adsorbent may be made using an adsorbentsheet wrapped with alternating layers of spacer material. Other formsinclude, but are not limited to wound extruded adsorbent sheets whereribs are molded directly into the adsorbent, thereby creating gas flowchannels. In another embodiment adsorbent sheets can be stacked on topof each other. Gas flow channels by mechanically spacing the adsorbentsheets with alternating layers of spacer material, or by molding ribsdirectly into the adsorbent sheet. The properties of the adsorbent sheetare such that no other supporting or containment fabric or material isneeded to maintain structural integrity or rigidity. Embodiments of suchforms are described in U.S. Pat. Nos. 5,964,221, 7,326,280, 7,329,307,8,413,655 and 8,685,153 all incorporated by reference in theirentireties.

In some embodiments, the sheets are wound into a cylinder but thecartridge may also be of other geometries. In the wound embodiments, thesheet 30 is spiraled (i.e., arranged in a continuous helix or asseparate rings or helixes arranged concentrically) as shown asillustrated in FIG. 1(a). Air flow through the cartridge can be fromboth directions (top to bottom, or bottom to top) and is parallel to thespiraled adsorbent sheet surfaces. FIG. 1(b) shows a top view ofcylindrical cartridge of FIG. 1(a) with adsorbent sheet 30 arranged in a“spiral” configuration within a canister 22 where the sheet is wrappedaround the center. FIG. 1(c) shows separating screens 32 positionedbetween the spirally positioned sheets 30 that allow gas flow throughthe space 34 between the sheets 30.

In some embodiments, the sheets are stacked into a cube or rectangularshape (90 degree corners on all sides but length, width and depth may ormay not be identical). In some embodiments, the adsorbent surfaces areplanar. The term “planar” used to describe surfaces means that theadsorbent surfaces are substantially without curvature (e.g., thesurfaces are not rolled). A sealing material (foam or rigid) may be usedto seal two or more sides of the cube or rectangle, leaving two open endfaces (to allow for air flow), two outer surfaces formed by theadsorbent sheets, and two foam surfaces.

In some embodiments, each adsorbent surface comprises the same type ofadsorbent. In other embodiments, each adsorbent surface is independentlyselected from various adsorbents.

In some embodiments, the adsorbent material used in the adsorbentsurfaces is calcium hydroxide or lithium hydroxide. Further descriptionof LiOH adsorbent sheets can be found in, for example, Hrycak et al. inU.S. Pat. Nos. 7,329,307 and 7,326,280, each of which is incorporatedherein by reference in its entirety. Further description of Ca(OH)₂adsorbent sheets and other types of adsorbent sheets can be found in,for example, in McKenna, U.S. Pat. No. 5,964,221, which is incorporatedherein by reference in its entirety.

In one embodiment shown in FIG. 1(d), sheet 30 is formed of an adsorbentfilled expanded porous polymer (e.g., PTFE) sheet having amicrostructure of nodes 40 interconnected with fibrils 41 whereinadsorbent material 39 is present in the voids of the polymer structureas taught by U.S. Pat. No. 4,985,296 issued to Mortimer, Jr.,incorporated herein by reference in its entirety. This sheet is waterrepellent, but air-permeable. Ideally, particles 39 are packed in amulti-modal (e.g., bi-modal or tri-modal) manner, with particles ofdifferent sizes interspersed around one another to fill as much of theavailable void space between particles as is possible so as to maximizethe amount of active material contained in the sheet. This techniquealso allows more than one type of adsorbent particle to be filled into asingle sheet. In some embodiments, the adsorbent sheet is made using athermally induced phase separated process.

In some embodiments, the sheet can be made using PTFE. By using filledporous expanded polytetrafluoroethylene (PTFE) as sheet 30 (or otherthermally induced phase separated polymer), a number of additionaladvantages are further imparted. Expanded PTFE is a non-limiting,non-out-gassing inert material that effectively reduces dusting ofadsorbent material during manufacturing and during the life of thefilter. Additionally, processing advantages of this material include theability to make a relatively thin material that can be produced in awide sheet and then cut (or cut and pleated) into desiredconfigurations.

The properties of CO₂ adsorbent filled polymer sheet are such that noother supporting fabric or material is needed to maintain structuralintegrity. In fact, not only can the adsorbent sheet withstand flexing,pleating and mechanical vibration under dry conditions, when PTFE isused, the hydrophobicity of the PTFE offers this structural durabilityeven while subjected to direct liquid water contact. Another embodimentof sheet 30 is shown in FIG. 1(e), where filled polymer sheet 30 isencapsulated between two hydrophobic gas-permeable membranes 42. Theseouter membranes 42 add extra protection to ensure that adsorptionmaterial 40 is contained within sheet 30 while preventing water fromreaching the adsorbent contained in the sheet. Membranes 42 must have ahigh degree of filtration efficiency to prevent adsorbent particles fromescaping into the breathing atmosphere. These membranes 42 preferablycomprise porous expanded polytetrafluoroethylene (PTFE), because it ishydrophobic and offers high particulate filtration efficiency.

A third embodiment of the sheet is shown in cut-away FIG. 1(f), where aninternal screen 43 is encapsulated by adsorbent material 39 that issurrounded by two hydrophobic gas-permeable membranes 42.

A fourth embodiment of the sheet 30 is shown in FIG. 1(g) where aninternal screen 44 is attached to two hydrophobic gas-permeablemembranes 42 and adsorbent material 39 is positioned in the voidsbetween screen members 44.

FIGS. 1(h) thorough 1(k) illustrate a method for making sheet 30 of FIG.1(g) having an internal screen 44, adsorbent material 39, and outermembranes 42. FIG. 1(h) depicts internal screen 44. Next, in FIG. 1(i),internal screen 44 is attached to a membrane 42 by a lamination process.Subsequently, in FIG. 1(j), adsorbent material 39 is added into the opencells of internal screen 44. Afterwards, in FIG. 1(k), a second membrane42 is laminated to the top of the internal screen 44, therebyencapsulating adsorbent material 40 within.

FIG. 1(l) is a scanning electron micrograph of another embodiment ofsheet 30 used in the cartridges described herein. This structure isproduced by way of thermally induced phase separation, such as in thefollowing manner.

A water repellent polymer, such as ultra high molecular weightpolyethylene, is combined with a gas adsorbent material, such as calciumhydroxide powder. This combination may be accomplished by combining thetwo materials together in an extruder. By conveying this mixture throughthe extruder and mixing with a lubricant, such as mineral oil, thepolymer dissolves in the lubricant and become uniformly mixed with theadsorbent and lubricant. This mixture can then be extruded into acomposite sheet or other shape.

The composite sheet may be calendared to further flatten the sheet ifdesired. The lubricant may then be extracted out of the resulting sheetusing a solvent, such as hexane. The solvent may then be removed, suchas through use of a dry nitrogen purge.

The resulting structure is highly micro-porous, allowing for thediffusion of CO₂ or other gases, and yet is able to be produced withvery high adsorbent powder loadings per unit volume. Additionally, if avery strong polymer, such as Ultra High Molecular Weight Polyethylene isused, a very small amount of polymer is required to make the sheetstructurally stable, which allows for even higher adsorbent loadings perunit volume. While typical powder loadings for this type ofmanufacturing process are on the order of 50 to 60% filler powder afterprocess oil extraction, loadings well above 60% may be possible. In someembodiments, adsorbent loading is greater or equal to about 90% byweight. In some embodiments, adsorbent loading is greater or equal toabout 97%. Additionally, in some embodiments, the material is moldedinto any desired shape, and thus, the separating means may beaccomplished by molding separating ribs onto the surface of the sheet.

Various embodiments of this molded structure are illustrated in FIGS.1(m) through 1(q). By molding the separating elements 33 (or “ribs”)directly out of adsorbent material, not only is the adsorbent cartridgeeasier to produce, but, because of its self-separating properties, thetotal amount of adsorbent in the filter can be increased by 10 to 30percent.

In some embodiments, the cartridge is formed from a self-supportingadsorbent sheet wound into a roll to form multiple layers mechanicallyspaced to provide gas flow channels between the layers from one end ofthe cartridge to the other (e.g., FIG. 3). For example, in someembodiments, the cartridge can be formed as in U.S. Pat. No. 5,964,221,which is incorporated herein by reference in its entirety.

In another embodiment, the cartridge is formed by a stack ofself-supporting adsorbent sheets mechanically spaced to provide gas flowchannels between the layers from one end of the cartridge to the other(e.g., FIG. 3a ). For example, the cartridge can be formed as describedin U.S. Pat. No. 8,685,153, which is incorporated herein by reference inits entirety. FIG. 3a shows an embodiment of a self-supported adsorbentcartridge 141 containing adsorbent sheets 30 in which multiple stakes142 and 143 (8 in the embodiment depicted in FIG. 3a ) are driven intothe adsorbent cartridge to securely hold the chemically reactiveadsorbent sheets together. A volume 145 demarcated by dashed lines isremoved from adsorbent cartridge 141 in FIG. 3a to expose stakes 142 and143. These stakes enable the cartridge to maintain its correct externaldimensions while simultaneously holding each sheet against the adjacentsheets. Alternatively, the adsorbent sheets can be staked with a stapleor staples, a wire, rod(s), a cord, rivet(s), or elastic materials. Therigid staked cartridge may be further wrapped with a thin polymer sleevesuch that the sleeve does not cover air inlet and outlet faces 146, 147of the adsorbent cartridge. This thin sleeve prevents the end user fromcontacting the adsorbent chemical. The sleeve provides little or noclamping forces to hold the adsorbent cartridge together.

In some embodiments no polymer sheet is wrapped around the cartridge.The stakes rigidly hold the sheets in place such that sheet to sheetcontact is maintained. As shown in FIG. 3(a) stakes 142 are insertedperpendicular to flow path 144 and additional cartridge stability can beachieved by inserting a stake or multiple stakes 143 at angles up to at90 degrees with respect to flow path 144, which reduce or eliminateflexing of the cartridge. Air inlet face 146 and air outlet face 147 ofcartridge 141 can be reversed should the direction of flow 144 bereversed. Cartridge 141 functions similarly for airflow from bothdirections.

Cartridge 141 can further include a wrap of polymer foam on four sidesof the cartridge to allow for sealing when cartridge 141 is installedinto a canister. The polymer foam could be installed by itself or overor under a polymer wrap.

Manufacture of Adsorbent Cartridges Having a Color Indicator

In some embodiments, any number of windows (or openings) may be cut intothe outermost layer of the adsorbent (“outermost layer”), in anyconfiguration. There may be a single line of windows (50) cut into theoutermost layer of the wound adsorbent sheet of the cartridge (51) inthe direction of gas flow in a straight line (FIG. 4), staggered, or atwo-dimensional checkerboard of windows, straight or staggered, or somecombination thereof. The windows may be of any dimension and each windowmay have its own dimension, independent of other windows. In oneembodiment of the present invention, the windows are aligned with thedirection of flow, and the window size is enlarged to provide for lessadsorbent mass in the channels thereby increasing the CO₂ contaminantlevels further down the cartridge, which provides for the ability to“tune” the time at which the indicator reacts and changes color.

Once the windows have been cut in the outermost layer, indicator may bepositioned on the adsorbent layer below the window in a variety of ways.A liquid coating of indicator may be applied to the layer beneath theoutermost layer below the window, in an area larger than the window. Forexample, a solution of roughly 1% ethyl violet and 0.05% NaOH in watercan be coated using a variety of methods using loadings from 1 to 20mg/cm². This application may turn violet on exposure to the basicsurface of a typical adsorbent (e.g., calcium hydroxide and 0.7 w/w %NaOH on a dry basis), but may turn back to the original white color ofthe adsorbent in less than a day (FIG. 5).

Instead of coating indicator on the layer beneath the window, one canplace a thin indicator layer below the window. The thin indicator layershould be thin so as to not make the wound cartridge out of round, or tocreate a bump in an orthoganol stack of adsorbent sheets. It may be 30mils or less or 20 mils or less, preferably 10 mils or less,

In another embodiment, the area below the window can be at leastpartially filled with a plug of indicating material. This is similar tothe indication layer approach, but in this case the plug has the sameareal dimensions as the window. The plug may not be as thick as thelayer that the window was cut out of.

In both the indicator layer and indicator plug embodiments, theindicator layer or plug may be composed of materials different from theadsorbent sheet layer. One example of the utility of this approach is toutilize the ethyl violet indicator dye in combination with calciumhydroxide and sodium hydroxide absorbent to make the plugs, which arethe inserted into windows in a cartridge composed of lithium hydroxide,thereby getting the cartridge performance of a lithium hydroxidecartridge, with the indicator chemistry of the calcium hydroxide/ethylviolet.

It is also possible to use other indicator materials for calciumhydroxide or lithium hydroxide carbon dioxide adsorbents. As describedin U.S. Pat. No. 3,068,073, activated alumina with thymol blue can beused to indicate the presence of carbon dioxide. Likewise U.S. Pat. No.5,124,129 describes a carbon dioxide indicator based on hydrophilicpolymer and the pH sensitive dye, o-cresolpthalein.

In all embodiments with windows (indicator coating, indicator layer andindicator plug), an outer transparent wrap may be placed over theoutermost layer of adsorbent sheet to hold the indicator in or under thewindow, and it is transparent so the indicator can be seen without gasescaping from the windows or plugged areas.

In another embodiment, stripes or other discontinuous geometric patternscan be coated onto the surface of the outer adsorbent layer of thecartridge.

The chemistry of the indicator system of the present invention can bevaried for any of the diverse applications. CO₂ adsorbents currently usea variety of indicators, such as ethyl violet, Titan yellow, Kenazolyellow, and the like. All of these indicators change with either the pHof the calcium hydroxide absorbent, which gets lower as the adsorbent isreacted, or by the dryness or water content of the adsorbent which isreduced after reacting with CO₂.

Other indicators that are used in other industrial applications may beutilized in the present invention, and include but are not limited toother specialty gas filtration application such as adsorbing water (U.S.Pat. No. 5,766,312), nitrogen, hydrogen, oxygen, petroleum processes andother industrial gas and liquid applications.

The present invention may also be used with adsorbent/indicator systemsfor hazardous materials as described in U.S. Pat. No. 4,326,514.

EXAMPLES Example 1

An extruded sheet (thickness 51 mils) with ribs (height 29 mils) wasmade using calcium hydroxide and 0.7 w/w % NaOH and 2.5 w/w % CaCl₂ (drybasis), as described in U.S. Pat. No. 5,964,221). The sheet was woundinto a cylindrical cartridge with dimensions 9.5 cm in diameter and 15cm in height. The sheet was sprayed with ethyl violet indicator (1 w/w %in water). This cartridge was placed in a Micropore Stein housing (PNRx0719a) designed to distribute airflow uniformly across the cartridgeinlet end. This was tested at conditions representing a typical surgery:10 liter/min tidal volume, 1 liter/min fresh gas flow, 10breaths/minute, 1:2 inspiratory/expiratory, 160 cc CO₂/min). Photographsduring the test demonstrate the superior uniformity of flow front withinan adsorbent cartridge (FIG. 6) compared with a granular bed (FIG. 2).

Example 2

A cylindrical adsorbent cartridge was prepared as per the instructionsof Example 1, but it was loaded with 19 w/w % water as it was wound byspraying 34 Mg/cm2 of water on the rib side as it was wound. An outertransparent layer was wrapped around the outside to hold the end of theouter wrap and the cartridge was allowed to sit for two days so that thewater could thoroughly wet the adsorbent. The outer transparent layerwas then cut, the outermost layer was peeled back and a series of fivewindows was cut into the outer wrap. Ethyl violet (1 w/w % in water) wasapplied to an area below the windows, on the layer beneath the outermostlayer. The loading of the ethyl violet solution was in the range ofapproximately 0.5-10 mg/cm2. The outer wrap was rewound and coveredagain with a transparent layer to hold it down (FIG. 5a ). After 24hours, the indicator turns white, which means the cartridge is ready foruse (FIG. 5b ). The cartridge was tested as described in Example 1 andphotographs were taken during the test, demonstrating how the windowsturn color as the adsorbent in the cartridge is consumed (FIG. 7). Fourof the five windows turned color by the time the test ended (outlet CO₂concentration 0.5%). Note that the indicator color did not revert for atleast 75 hours (FIG. 8).

EMBODIMENTS

1. An adsorbent cartridge for removing gaseous carbon dioxidecontaminants, comprising a self-supporting adsorbent sheet wound into aroll to form multiple layers mechanically spaced to provide gas flowchannels between the layers from one end of the cartridge to the other,wherein the sheet is formed from a mixture comprising polymer and anadsorbent material comprising calcium hydroxide or lithium hydroxide,wherein the cartridge further comprises a color indicator for visuallyindicating consumption of the adsorbent to an external observer, whereinat least one area of color indicator is visually exposed to an externalobserver while the cartridge is in use.

2. An adsorbent cartridge for removing gaseous carbon dioxidecontaminants, comprising a self-supporting adsorbent sheet wound into aroll to form multiple layers mechanically spaced to provide gas flowchannels between the layers from one end of the cartridge to the other,wherein the sheet is formed from a mixture comprising polymer and anadsorbent material comprising calcium hydroxide or lithium hydroxide,wherein the cartridge further comprises a color indicator for visuallyindicating consumption of the adsorbent to an external observer, whereinat least one area of color indicator is visually exposed to an externalobserver while the cartridge is in use, wherein the total surface areaof the visually exposed areas of color indicator are equal to or lessthan the total surface area of the outermost layer of the cartridge.

3. An adsorbent cartridge for removing gaseous carbon dioxidecontaminants, comprising a self-supporting adsorbent sheet wound into aroll to form multiple layers mechanically spaced to provide gas flowchannels between the layers from one end of the cartridge to the other,wherein the sheet is formed from a mixture comprising polymer and anadsorbent material comprising calcium hydroxide or lithium hydroxide,wherein the cartridge further comprises a color indicator for visuallyindicating consumption of the adsorbent to an external observer, whereinat least one area of color indicator is visually exposed to an externalobserver while the cartridge is in use, wherein the total surface areaof all color indicator in the cartridge is equal to or less than thetotal surface area of the outermost layer of the cartridge and whereinthe total surface area of the visually exposed areas of color indicatoris equal to or less than the total surface area of all color indicatorin the cartridge.

4. The adsorbent cartridge of claim 3 or 4, wherein the total surfacearea of all color indicator in the cartridge is 0.05% to 50% of thesurface area of the outermost layer.

5. The adsorbent cartridge of claim 3 or 4, wherein the color indicatoris applied to one or more layers of the cartridge solely on the outerside of the adsorbent sheet, wherein one or more discrete areas of colorindicator are visible to external observer or are exposed visually to anexternal observer through windows cut into the outermost layer.

6. The adsorbent cartridge of claim 3 or 4, wherein the color indicatoris applied to an indicator layer sandwiched between the outermost layerand the layer beneath the outermost layer, wherein one or more discreteareas of color indicator are exposed visually to external observerthrough windows cut into the outermost layer.

7. The adsorbent cartridge of claim 3 or 4, wherein the color indicatoris applied to a plug of material at least partially filling one or morewindows cut into the outermost layer, thereby visually exposing one ormore discrete areas of color indicator to an external observer.

8. The adsorbent cartridge of any one of claims 1-7, wherein thecartridge is for use in an anesthesia breathing circuit.

9. The adsorbent cartridge of any one of claims 1-8, wherein themultiple layers are mechanically spaced by parallel, longitudinal ribsmolded out of the sheet.

10. The adsorbent cartridge of any one of claims 1-8, wherein the layersare mechanically spaced by additional spacer material.

11. The adsorbent cartridge of any one of claims 1-10, wherein theadsorbent material comprises calcium hydroxide.

12. The adsorbent cartridge of any one of claims 1-10, wherein theadsorbent material comprises lithium hydroxide.

13. The adsorbent cartridge of any one of claims 1-13, wherein theadsorbent material further comprises sodium hydroxide, potassiumhydroxide, calcium chloride, or lithium hydroxide.

14. The adsorbent cartridge of any one of claims 1-14, furthercomprising a transparent film covering the outermost layer of thecartridge.

15. The adsorbent cartridge of any one of claims 1-15, wherein the colorindicator comprises ethyl violet, Titan yellow, Kenazol yellow,activated alumina with thymol blue, or o-cresolpthalein.

16. The adsorbent cartridge of claim 5, wherein the adsorbent materialcomprises calcium hydroxide and wherein the one or more discrete areasof color indicator visible to external observer are applied to theoutermost layer of the cartridge.

17. The adsorbent cartridge of claim 16, wherein the multiple layers aremechanically spaced by parallel, longitudinal ribs molded out of thesheet.

18. The adsorbent cartridge of claim 16 or 17, wherein the colorindicator comprises ethyl violet, Titan yellow, Kenazol yellow,activated alumina with thymol blue, or o-cresolpthalein.

19. The adsorbent cartridge of claim 16 or 17, wherein the colorindicator comprises ethyl violet.

20. The adsorbent cartridge of any one of claims 16-19, wherein thecartridge is for use in an anesthesia breathing circuit.

21. The adsorbent cartridge of claim 5, wherein the adsorbent materialcomprises calcium hydroxide and wherein the color indicator is appliedto the layer beneath the outermost layer of the cartridge and the one ormore discrete areas of the color indicator are exposed visually to theexternal observer by windows cut in the outermost layer of thecartridge.

22. The adsorbent cartridge of claim 21, wherein the multiple layers aremechanically spaced by parallel, longitudinal ribs molded out of thesheet.

23. The adsorbent cartridge of claim 21 or 22, wherein the colorindicator comprises ethyl violet, Titan yellow, Kenazol yellow,activated alumina with thymol blue, or o-cresolpthalein.

24. The adsorbent cartridge of claim 21 or 22, wherein the colorindicator comprises ethyl violet.

25. The adsorbent cartridge of any one of claims 21-24, wherein thecartridge is for use in an anesthesia breathing circuit.

26. The adsorbent cartridge of claim 6, wherein the multiple layers aremechanically spaced by parallel, longitudinal ribs molded out of thesheet.

27. The adsorbent cartridge of claim 26, wherein the color indicatorcomprises ethyl violet, Titan yellow, Kenazol yellow, activated aluminawith thymol blue, or o-cresolpthalein.

28. The adsorbent cartridge of claim 27, wherein the color indicatorcomprises ethyl violet.

29. The adsorbent cartridge of any one of claims 26-28, wherein thecartridge is for use in an anesthesia breathing circuit.

30. The adsorbent cartridge of any one of claims 26-29, wherein theindicator layer is 30 mils or less in thickness.

31. The adsorbent cartridge of any one of claims 26-29, wherein theindicator layer is 20 mils or less in thickness.

32. The adsorbent cartridge of any one of claims 26-29, wherein theindicator layer is 10 mils in thickness.

33. The adsorbent cartridge of any one of claims 26-32, wherein theindicator layer is formed from a mixture comprising calcium hydroxide,sodium hydroxide, and a polymer, to which the color indicator has beenapplied.

34. The adsorbent cartridge of claim 33, wherein the color indicator isethyl violet.

35. The adsorbent cartridge of claim 33 or 34, wherein the adsorbentmaterial comprises lithium hydroxide.

36. The adsorbent cartridge of claim 26, having a single window, whereinthe indicator layer has a single discrete area of the color indicatorpositioned to center on the window in the outermost layer of thecartridge.

37. The adsorbent cartridge of claim 36, wherein the indicator layer isformed from a mixture of calcium hydroxide, sodium hydroxide, and apolymer, to which the discrete area of color indicator has been applied.

38. The adsorbent cartridge of claim 37, wherein the color indicator isethyl violet.

39. The adsorbent cartridge of claim 38, wherein the adsorbent materialcomprises lithium hydroxide.

40. The adsorbent cartridge of claim 26, having multiple windows,wherein the indicator layer has multiple discrete areas of the colorindicator positioned to center on the windows in the outermost layer ofthe cartridge.

41. The adsorbent cartridge of claim 40 wherein the indicator layer isformed from a mixture of calcium hydroxide, sodium hydroxide, and apolymer, to which the discrete areas of color indicator have beenapplied.

42. The adsorbent cartridge of claim 41, wherein the color indicator isethyl violet.

43. The adsorbent cartridge of claim 42, wherein the adsorbent materialcomprises lithium hydroxide.

44. The adsorbent cartridge of claim 26, having multiple windows,wherein the indicator layer is a strip positioned such that the areaexposed by each window is covered by said strip, thereby exposing thecolor indicator to said external observer.

45. The adsorbent cartridge of claim 44, wherein the strip is formedfrom a mixture of calcium hydroxide, sodium hydroxide, and a polymer, towhich the color indicator has been applied.

46. The adsorbent cartridge of claim 45, wherein the color indicator isethyl violet.

47. The adsorbent cartridge of claim 46, wherein the adsorbent materialcomprises lithium hydroxide.

48. The adsorbent cartridge of claim 26, having multiple windows,wherein a separate indicator layer patch is utilized for each window.

49. The adsorbent cartridge of claim 48, wherein the indicator layer isformed from a mixture of calcium hydroxide, sodium hydroxide, and apolymer, to which the discrete areas of color indicator have beenapplied.

50. The adsorbent cartridge of claim 49, wherein the color indicator isethyl violet.

51. The adsorbent cartridge of claim 50, wherein the adsorbent materialcomprises lithium hydroxide.

52. The adsorbent cartridge of claim 7, wherein the multiple layers aremechanically spaced by parallel, longitudinal ribs molded out of thesheet.

53. The adsorbent cartridge of claim 52, wherein the plug has the sameareal dimensions as each window.

54. The adsorbent cartridge of claim 53, wherein the indicator layer isformed from a mixture of calcium hydroxide, sodium hydroxide, and apolymer, to which the color indicator has been applied.

55. The adsorbent cartridge of claim 54, wherein the color indicator isethyl violet.

56. The adsorbent cartridge of claim 54, wherein the color indicatorcomprises Titan yellow, Kenazol yellow, activated alumina with thymolblue, or o-cresolpthalein.

57. The adsorbent cartridge of 55 or 56, wherein the adsorbent materialcomprises lithium hydroxide.

58. The adsorbent cartridge of any one of claims 52-57, wherein the plugis 0.004 to 0.1 in thickness.

59. The adsorbent cartridge of any one of claims 16-58, furthercomprising a transparent film covering the outermost layer of thecartridge.

60. An adsorbent cartridge for removing gaseous carbon dioxidecontaminants, comprising a stack of self-supporting adsorbent sheetsmechanically spaced to provide gas flow channels between the layers fromone end of the cartridge to the other, wherein the sheet is formed froma mixture comprising polymer and an adsorbent material comprisingcalcium hydroxide or lithium hydroxide, wherein the cartridge furthercomprises a color indicator for visually indicating consumption of theadsorbent to an external observer, wherein at least one area of colorindicator is visually exposed to an external observer while thecartridge is in use, wherein the total surface area of all colorindicator in the cartridge is equal to or less than the total surfacearea of the outermost layer of the cartridge and wherein the totalsurface area of the visually exposed areas of color indicator is equalto or less than the total surface area of all color indicator in thecartridge.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An adsorbent cartridge for removing gaseous contaminants, comprising layers of one or more self-supporting adsorbent sheets mechanically spaced to provide gas flow channels between the layers from one end of the cartridge to the other, wherein the cartridge further comprises a color indicator for visually indicating consumption of the adsorbent to an external observer, wherein the color indicator is applied to one or more areas of an outermost layer of the adsorbent sheets of the adsorbent cartridge.
 2. The adsorbent cartridge of claim 1, wherein the cartridge is formed from a single self-supporting adsorbent sheet wound into a roll to form multiple layers.
 3. The adsorbent cartridge of claim 1, wherein the cartridge is formed from a stack of the self-supporting adsorbent sheets.
 4. The adsorbent cartridge of claim 1, wherein the sheet is formed from a mixture comprising an adsorbent material.
 5. The adsorbent cartridge of claim 4, wherein the sheet is formed from a mixture comprising polymer and the adsorbent material.
 6. The adsorbent cartridge of claim 4, wherein the adsorbent material comprises calcium hydroxide or lithium hydroxide.
 7. The adsorbent cartridge of claim 1, wherein the color indicator comprises ethyl violet, Titan yellow, Kenazol yellow, activated alumina with thymol blue, or o-cresolpthalein.
 8. The adsorbent cartridge of claim 1, wherein the total surface area of all color indicator in the cartridge is 0.05% to 50% of the surface area of the outermost layer.
 9. The adsorbent cartridge of claim 1, wherein the color indicator is applied to the outermost layer of the adsorbent sheets of the adsorbent cartridge by spraying the color indicator onto the outermost layer of the adsorbent sheets of the adsorbent cartridge.
 10. The adsorbent cartridge of claim 1, wherein the layers are mechanically spaced by parallel, longitudinal ribs molded out of the sheet.
 11. An anesthesia breathing circuit comprising the adsorbent cartridge of claim
 1. 12. An underwater breathing apparatus comprising the adsorbent cartridge of claim
 1. 